Various situations arise wherein one seeks to pump a liquid or gas from a pressurized source, such as a flow line, and output the fluid to a downstream container, such as a sample bottle. The sample bottle may, for example, be periodically sent to a laboratory for analysis to determine the BTU content of the sampled fluid, and thereby determine the BTU content of the gas flowing in the pressurized line. In many situations, a separate power source, such as an electric pump or pressurized hydraulic line, is readily available for driving the pump. In other situations typified by remole applications, a separate power source is not readily available or is not cost-effective for driving or powering the pump. In these latter situations, the pressured source can be used to drive the pump, thereby avoiding the expenses associated with a separate power supply. Prior art sampling pumps have been powered by an operator unit which receives pressure from the pressurized source, and which uses the; pressure as the driving force. Examples of sampling pumps which may utilize the pressurized line as the driving force for the pump operator are disclosed in U.S. Pat. Nos. 4,928,536 and 5,032,063.
Many of the advantages of a sampling pump powered by a fluid pressure source frequently are not realized if the fluid is contaminated with particles, such as rust, scale, or other particulate. The fluid ideally is filtered before entering the pump to reduce maintenance costs, and this filter ideally is closely adjacent the pump inlet port check valve. If the fluid line to the pump operator unit is not also filtered, however, service costs for the operator unit can become excessive. Service personnel periodically change the pump inlet filter, and may not inspect or change the pump operator filter.
In some applications, the pump inlet filter may be cleaned by the fluid itself, as disclosed in U.S. Pat. No. 5,074,154. Much of the fluid flowing to a sampling pump may thus pass by, rather than through, the pump inlet filter in a "hot loop", thereby continually cleaning the pump inlet filter. In other applications, this hot loop technique is not feasible, and substantially all fluid flow to the pump is input and discharged from the pump.
In many applications, a check valve is provided within the flow line downstream from the sampling pump. When used for gas applications, the pump discharge check valve ideally is closely adjacent the pump plunger, thereby minimizing the "dead areas" within the pumping system and improving pump efficiency, as disclosed in U.S. Pat. No. 5,074,154.
U.S. Pat. No. 5,191,801 discloses an improved fluid sampling pump including a line pressure driven actuator for pumping low pressure fluid to a sample container. The pump disclosed in this patent is not designed for pumping line fluid under a high pressure, e.g., 500 psi. Moreover, if line pressure increases considerably by, for example, 200 psi, the higher pressure fluid could pass through the pump to unintentionally fill the sample container. While line pressure to the actuator conceptually may be reduced, various practical problems are encountered when placing a pressure regulator between the pump bore and the actuator. A regulator of the type disclosed in U.S. Pat. No. 5,098,438 cannot be easily supported structurally by the pump body. Water in the fluid line may condense in the pressure regulator, thereby adversely affecting the operation of the regulator and/or the downstream pump actuator. Another problem with prior art sampling pumps relates to the life of the pump piston seal, particularly when the pump is being used for pumping various types of fluids normally deleterious to conventional O-ring materials.
The disadvantages of the prior art are overcome by the present invention, and a novel pump is hereinafter disclosed to satisfy the need for a reliable pump which may be used for various applications.